Heat engines and associated methods of producing mechanical energy and their application to vehicles

ABSTRACT

A closed cycle gas turbine system ( 40 ) comprising system comprising a compressor ( 52 ) for producing compressed gas, a gas turbine ( 42 ) for receiving the compressed gas, a heat storage means ( 44 ) having a first heat transfer means and adapted to receive the compressed gas from the compressor ( 52 ) and transmit the compressed gas to the gas turbine ( 42 ) and a second heat transfer means ( 46 ) for receiving exhaust gas from the gas turbine ( 42 ) and transmitting it to the compressor ( 52 ) and wherein the second heat transfer means ( 46 ) is adapted to transfer at least some heat from the exhaust gas prior to it being transferred to the compressor ( 52 ).

FIELD OF THE INVENTION

[0001] The present invention relates to heat engines, in particularengines which operate in accordance with the Carnot and Brayton cycles.More specifically, the present invention relates to new applications ofthese engines.

BACKGROUND TO THE INVENTION

[0002] One of the dangers of underground mining is that if part of themine collapses people who are working underground may be crushed orsuffocated. Suffocation in such a situation can occur because personnelare enclosed in a confined space so that they only have a limited supplyof oxygen. However, because it is typically necessary to provide aconstant supply of oxygen to tunnels which run through an undergroundmine, suffocation can also occur if the supply of oxygen to a tunnel iscut off.

[0003] It is therefore important to evacuate persons that have beentrapped underground as a result of a collapse in a mine, as quickly aspossible. One way of facilitating quick evacuation is to have a vehicleon standby which is capable of going down into the mine and rescuingsurvivors. These vehicles are typically referred to as MRVs. However,because oxygen is typically in short supply in the event of a collapseit is important that these vehicles are capable of operating in anoxygen depleted or free environment.

[0004] It is therefore desirable to provide an engine which is capableof operating in an oxygen depleted or free environment. It is alsodesirable to provide a vehicle which is capable of operating in anoxygen free or depleted environment.

SUMMARY OF THE INVENTION

[0005] In a first aspect the present invention provides a reciprocatingengine comprising a compartment having two adjacent first and second subcompartments and at least one moveable partition, the at least onemoveable partition being arranged for movement to vary the volume of theadjacent sub compartments, the engine including heat storage means forheating a first gas which is contained within the first sub compartmentrelative to a second gas which is contained within the second subcompartment, the engine including first heat transferral means fortransferral of heat from the heat storage means to the first gas, the atleast one moveable partition being arranged to cyclically vary thevolume in the adjacent sub compartments as a result of heating of thefirst gas and consequently produce mechanical energy, wherein the engineincludes gas cycling means for cycling the first gas cyclically from thefirst adjacent sub compartment to the first heat transferral means.

[0006] In a second aspect the present invention provides a method ofproducing mechanical energy, the method comprising the steps of:

[0007] (a) providing a reciprocating engine comprising a compartmenthaving two adjacent sub compartments and at least one moveablepartition, the at least one moveable partition being arranged formovement to vary the volume of the sub compartments, the engineincluding heat storage means for heating a first gas which is containedwithin a first adjacent sub compartment relative to a second gas whichis contained within a second adjacent sub compartment, the engineincluding first heat transfer means for transferral of heat from theheat storage means to the first gas, the at least one moveable partitionbeing arranged to cyclically vary the volume in the adjacent subcompartments as a result of heating of the first gas and consequentlyproduce mechanical energy; and

[0008] (b) cycling the first gas from the first adjacent sub compartmentto the first heat transferral means.

[0009] In a third aspect the present invention provides a closed cyclegas turbine engine comprising a compressor for compressing gas which isfed into an inlet side of the turbine, and heat storage means andassociated first heat transfer means for transferring heat from the heatstorage means to the gas either prior to it entering the turbine or uponentry of the gas to the turbine, the gas turbine engine being arrangedto feed exhaust gas of the gas turbine into the compressor, wherein theengine includes second heat transfer means for transferring heat fromthe exhaust gas to the compressed gas, prior to it being pumped throughthe first heat transfer means.

[0010] In a fourth aspect the present invention provides a closed cyclegas turbine engine comprising a compressor for compressing gas which isfed into an inlet side of the turbine, and heat storage means andassociated primary heat transfer means for transferring heat from theheat storage means to the gas either prior to it entering the turbine orupon entry of the gas to the turbine, the gas turbine engine beingarranged to feed exhaust gas of the gas turbine into the compressor,wherein the engine includes secondary heat transfer means for removal ofheat from the exhaust gas prior to it being pumped through thecompressor.

[0011] In a fifth aspect the present invention provides a method ofproducing mechanical energy, the method comprising the steps of:

[0012] (a) providing a closed cycle gas turbine engine comprising acompressor for compressing gas which is fed into an inlet side of theturbine, and heat storage means and associated first heat transfer meansfor transferring heat from the heat storage means to the gas eitherprior to it entering the turbine or upon entry of the gas to theturbine, the gas turbine engine being arranged to feed exhaust gas ofthe gas turbine into the compressor; and

[0013] (b) transferring heat from the exhaust gas to the compressed gasprior to it being pumped through the first heat transfer means.

[0014] In a sixth aspect the present invention provides a method ofproducing mechanical energy, the method comprising the steps of:

[0015] (a) providing a closed cycle gas turbine engine comprising acompressor for compressing gas which is fed into an inlet side of theturbine, and heat storage means and associated primary heat transfermeans for transferring heat from the heat storage means to the gaseither prior to it entering the turbine or upon entry of the gas to theturbine, the gas turbine engine being arranged to feed exhaust gas ofthe gas turbine into the compressor; and

[0016] (b) transferring heat from the exhaust gas prior to it beingpumped through the compressor.

[0017] In a seventh aspect the present invention provides a vehicleincluding a land vehicle, marine vehicle or aircraft wherein the vehicleincludes the engine of the first, third or fourth aspect of the presentinvention.

[0018] According to a further aspect of the present invention there isprovided a reciprocating engine comprising a container having acompartment with adjacent first and second sub-compartments, separatedby a moveable partition, an inlet and an outlet, a heat storage means, aheat transfer means and a conduit system interconnecting the outlet withthe heat transfer means and the heat transfer means with the inlet,wherein heat from the heat storage means is adapted to be transferred bythe heat transfer means to gas within the conduit to drive the moveablepartition to cyclically vary the volume in the adjacent sub-compartmentsto enable cyclical circulation of gas through the conduit system and theproduction of mechanical or electrical energy.

[0019] Preferably the reciprocating engine operates in accordance withthe sterling cycle which is composed of four distinct thermodynamicprocesses which include isothermal compression, constant volume heating,isothermal expansion and constant volume cooling.

[0020] It is preferred that the conduit system comprises a conduitconnected at one end to the outlet which is located at an approximatemid-point of the container and at its opposite end to the heat transfermeans.

[0021] Preferably the conduit system also includes a conduit connectedto the inlet which is located at one end of the container and at theopposite end to an outlet of the heat transfer means.

[0022] It is preferred that a regenerator is connected in the conduitsystem between the heat transfer means and the outlet of the cylinder.

[0023] The vehicle may include a MRV.

[0024] The heat storage means may be a heat storage cell.

[0025] The heat storage cell may be a liquid salt heat storage cell.

[0026] The liquid salt heat storage cell may be a sodium chloride(NACL), lithium fluoride (LIF), or sodium fluoride (NAF) liquid saltheat storage cell.

[0027] The liquid salt heat storage cell used to power an MRV ispreferably capable of providing 1000 KW of stored energy at atemperature ranging from 650 to 1000 degrees C. The preferred weight ofthe NACL, LIF or NAF liquid salt heat storage cell is therefore 3.96,2.35 or 2.97 tonnes respectively.

[0028] The heat storage means may be arranged to maintain the first gasof the reciprocating engine at a temperature of approximately 650° C.

[0029] The reciprocating engine may include second heat transferralmeans for transferral of heat from the second adjacent compartment.

[0030] The second heat transferral means may be arranged to maintain thesecond adjacent sub compartment at a temperature of approximately 15° C.

[0031] Alternatively, the heat storage means and first heat transferralmeans may be arranged to maintain the first adjacent sub compartment ofthe reciprocating engine at a temperature of greater than approximately700° C. and the second heat transferral means may be arranged tomaintain the second adjacent compartment of the reciprocating engine atapproximately room temperature.

[0032] The first heat transferral means may include a first heatexchanger.

[0033] The first heat exchanger may be formed out of incanel or 253temperature resistant stainless steel.

[0034] The second heat transferral means may include a second heatexchanger.

[0035] The method of the second aspect of the present invention mayfurther include the step of heating the first adjacent sub compartmentso that the temperature of the first adjacent sub compartment is 600° C.hotter than the second adjacent sub compartment.

[0036] The first and/or second heat exchanger may include a third gas.

[0037] The first and second gases may be the same as the third gas.

[0038] The first and second gases may be Air, Ammonia, Argon, CarbonDioxide, Carbon Monoxide, Helium, Hydrogen, Methane, Oxygen, or WaterVapour and are preferably helium.

[0039] If the first and second gases are different to the third gas, thethird gas is preferably Hydrogen.

[0040] The third gas may comprise the first gas wherein the first heatexchanger operates by passage of the first gas through the first heatexchanger.

[0041] The third gas is preferably high-pressure gas having a pressureranging from approximately 15 megapascals to 25 megapascals.

[0042] The gas cycling means may include a pipe.

[0043] The reciprocating engine may include a regenerator, theregenerator comprising heat absorption and release means for cyclicallyabsorbing heat from the first gas and subsequently transferring heat tothe first gas upon cooling of the first gas.

[0044] The regenerator may further include a first and second adjacentcompartment connecting portion which is arranged to transfer the firstand second gases between the first and second adjacent sub compartments.

[0045] Alternatively, the regenerator may further include a heatabsorbing member and a pipe, the pipe being arranged to transfer thefirst gas from one part of the first adjacent sub compartment, throughthe heat absorbing member, and subsequently to another part of the firstadjacent sub compartment.

[0046] The reciprocating engine may include combined gas cycling andregenerator means for performing the combined function of the gascycling means and the regenerator, the combined gas cycling andregenerator means having the heat absorption and release means of theregenerator and the first heat exchanger of the first heat transferralmeans, the combined gas cycling and regenerator means being arranged topass the first gas sequentially through the heat absorption and releasemeans, and first heat exchanger prior to reentering the first adjacentsub compartment.

[0047] The first gas may be arranged to cycle from the first adjacentsub compartment to the first heat transferral means, heat absorption andrelease means, or combined first gas cycling and regenerator means underbuoyancy effects of heat to result in the first gas being cycled to andfrom the first adjacent sub compartment by convection.

[0048] The reciprocating engine may include pump means for pumping thefirst gas to and/or from the first heat transferral means, heatabsorption and release means, or combined gas cycling and regeneratormeans.

[0049] The at least one moveable partition may be a single moveablepartition which is arranged to divide the compartment into the twoadjacent sub compartments, the single moveable partition being arrangedto substantially sealingly engage the compartment so that the first gasis prevented from mixing with the second gas.

[0050] The compartment may be an elongated compartment and the singlemoveable partition may be orientated substantially transversely to alongitudinal axis of the compartment and arranged to move along thelongitudinal length of the compartment.

[0051] The reciprocating engine may include a displacer for displacementof the first gas, the displacer being arranged to move in relationshipwith the at least one moveable partition.

[0052] The displacer may be arranged to move within the elongatedcompartment and may be arranged to move along the longitudinal length ofthe compartment, the displacer being arranged to move 90° out of phaseto the single moveable partition.

[0053] Alternatively, the at least one moveable partition may comprisefirst and second moveable partitions which are arranged to substantiallysealingly engage the first and second adjacent sub compartmentsrespectively, the first and second gases being free to mix.

[0054] The first and second gases may be free to mix by passage througha regenerator.

[0055] The method of the second aspect of the present invention mayfurther include the step of cycling the first gas out of the firstadjacent sub compartment, through the first heat exchanger andsubsequently back into the first adjacent sub compartment.

[0056] The method of the second aspect of the present invention mayfurther include the step of cycling the first gas through theregenerator prior to the passage of the first gas through the first heatexchanger.

[0057] The method of the second aspect of the present invention mayfurther include the step of cycling the first gas under buoyancy effectsof heat to result in the first gas being cycled by convection.

[0058] Alternatively, the method of the second aspect of the presentinvention may further include the step of pumping the first gas throughthe first heat exchanger and/or regenerator.

[0059] The gas cycling means may include flow control means forcontrolling the flowrate of the first gas cycling from the firstadjacent sub compartment to the first heat transferral means.

[0060] The flow control means is preferably arranged to control theflowrate of the first gas cycling from the first adjacent subcompartment rather than controlling the flowrate of the first gas whichis returning to the first adjacent sub compartment.

[0061] The flow control means is preferably arranged to control theflowrate of the first gas cycling to the regenerator.

[0062] The flow control means may comprise a valve.

[0063] The flow control means may comprise a butterfly valve.

[0064] The method the second aspect of the present invention may furtherinclude the step of controlling the flowrate of the first gas whichcycles from the first adjacent sub compartment to the first heattransferral means.

[0065] The method of the second aspect of the present invention mayfurther include the step of controlling the flowrate of the gas whichcycles from the first adjacent sub compartment to the first heattransferral means via the flow control means.

[0066] The third aspect of the present invention may include thesecondary heat transfer means.

[0067] The fourth aspect of the present invention may include the secondheat transfer means.

[0068] The fifth aspect of the present invention may further include thestep of transferring heat from the exhaust gas prior to it being pumpedthrough the compressor.

[0069] The sixth aspect of the present invention may further include thestep of transferring heat from the exhaust gas to the compressed gasprior to it being pumped through the primary heat transfer means.

[0070] According to a further aspect of the present invention there isprovided a closed cycle gas turbine system comprising a compressor forproducing compressed gas, a gas turbine for receiving the compressedgas, a heat storage means having a first heat transfer means and adaptedto receive the compressed gas from the compressor and transfer thecompressed gas to the gas turbine, a second heat transfer means forreceiving exhaust from the gas turbine and transmitting it to thecompressor and wherein the second heat transfer means is adapted totransfer heat from the exhaust gas prior to it being transferred to thecompressor.

[0071] Preferably the second heat transfer means is adapted to transferheat from the exhaust gas to the compressed gas prior to it beingreceived by the heat storage means.

[0072] Preferably the second heat transfer means comprises a heatexchanger.

[0073] The second heat transfer means may include a recuperator.

[0074] The compressor of the gas turbine engine may be arranged tocompress the gas according to the ratio of 6.2:1.

[0075] The heat storage means and associated first and primary heattransfer means of the gas turbine engine may be arranged to maintain thetemperature of gas entering the gas turbine at a relatively constanttemperature of approximately 930° C.

[0076] The gas turbine engine may be a humid gas turbine engine whichincludes liquid injection means for injecting liquid into the compressedgas after it leaves the compressor and before it is heated by the firstor primary heat transfer means, and liquid condensing means forsubsequently condensing liquid from the exhaust gas prior to it beingfed into the compressor.

[0077] The liquid may be condensed from the exhaust gas either before orafter the exhaust gas passes through the secondary heat transfer means.

[0078] The liquid injected by the liquid injection means may be selectedso that the liquid condensing means is not required because the liquidautomatically condenses from the exhaust gas.

[0079] The liquid injected by the liquid injection means may be selectedso that the second heat transfer means reduces the temperature of theexhaust gas to approximately ambient temperature prior to it passinginto the compressor, without the use of the secondary heat transfermeans.

[0080] The liquid may comprise water and preferably comprises distilledwater.

[0081] The compressor of the humid gas turbine engine is preferablyarranged to compress the gas according to a ratio greater than or equalto approximately 15:1.

[0082] The compressor may be arranged to compress the gas according to aratio of less than or equal to approximately 30:1.

[0083] The gas turbine may be greater than or equal to a 1MW turbine.

[0084] The compressor and first or primary heat transfer means may bearranged so that the temperature of the compressed gas exiting thecompressor is approximately 400° C. and so that the liquid injectionmeans reduces the temperature of the compressed gas to approximately195° C.

[0085] The methods of the fifth and sixth aspects of the presentinvention may further include the step of heating the gas either priorto the gas entering the gas turbine or upon entry of the gas to the gasturbine to maintain the temperature of gas entering the gas turbine at arelatively constant temperature of approximately 930° C.

[0086] The methods of the fifth and sixth aspects of the presentinvention may further include the steps of:

[0087] (a) injecting liquid into the compressed gas after it leaves thecompressor and before it is heated by the first or primary heat transfermeans; and

[0088] (b) condensing the liquid from the exhaust gas prior to it beingfeed into the compressor.

[0089] The first and primary heat transfer means may each include aprimary heat exchanger, the primary heat exchanger being arranged totransfer heat from the heat storage means to the compressed gas uponpumping of the compressed gas through the primary heat exchanger, thecompressor being arranged to pump the compressed gas through the primaryheat exchanger.

[0090] Compressed gasses having a high specific heat capacity result inhigh power output from the gas turbine engine, however they are not asefficient as gasses with lower specific heat capacities because theyretain more heat when exhausted from the turbine. Therefore, the gas ofthe gas turbine engine may be Air, Ammonia, Argon, Carbon Dioxide,Carbon Monoxide, Helium, Hydrogen, Methane, Oxygen, or Water Vapour andis preferably helium.

[0091] The primary heat exchanger may be arranged to raise thetemperature of the compressed gas to greater than or equal toapproximately 900° C.

[0092] The methods of the fifth and sixth aspects of the presentinvention may further include the step of transferring heat from theheat storage means to the compressed gas using the primary heatexchanger.

[0093] The second heat transfer means may be arranged to decrease thetemperature of the exhaust gas to approximately 200° C. and increase thetemperature of gas exiting the compressor to approximately 400° C.

[0094] The second heat transfer means may include a recuperator.

[0095] The recuperator may include a secondary heat exchanger.

[0096] The secondary heat transfer means may be arranged to remove heatfrom the exhaust gas after the exhaust gas has passed through the secondheat transfer means.

[0097] The secondary heat transfer means may be arranged to decrease thetemperature of the exhaust gas to approximately 30° C.

[0098] The secondary heat transfer means may include a tertiary heatexchanger.

[0099] The tertiary heat exchanger may include liquid cooling means forpassage of cooling liquid through the tertiary heat exchanger forremoval of heat from the exhaust gas.

[0100] The methods of the fifth and sixth aspects of the presentinvention may further include the step of transferring heat from theexhaust gas to the compressed gas prior to the compressed gas beingpumped through the first or primary heat transfer means using therecuperator.

[0101] The methods of the fifth and sixth aspects of the presentinvention may further include the step of transferring heat from theexhaust gas prior to the exhaust gas being pumped through the compressorusing the tertiary heat exchanger.

[0102] The gas turbine engine of the third and fourth aspects of thepresent invention may further include gas flowrate control means forcontrolling the flowrate of gas flowing through the gas turbine engine.

[0103] The gas flowrate control means may be arranged to throttle thegas turbine engine to control its power output by restricting theflowrate of gas flowing through the gas turbine engine.

[0104] The gas flowrate control means may include a valve.

[0105] The gas flowrate control means may be positioned to control theflowrate of gas flowing between the secondary heat transfer means andthe compressor.

[0106] The method of the fifth and sixth aspects of the presentinvention may further include the step of controlling the flowrate ofgas flowing through the gas turbine engine to throttle the gas turbineengine and control its power output.

[0107] The method of the fifth and sixth aspects of the presentinvention may further include the step of controlling the flowrate ofgas flowing through the gas turbine engine using the gas flowratecontrol means.

[0108] The gas turbine engine of the third and fourth aspects of thepresent invention may further include liquid flowrate control means forcontrolling the flowrate of liquid which is injected into the compressedgas by the liquid injection means, to control the power output of thegas turbine engine.

[0109] The liquid flowrate control means may comprise a proportionalintegral differential (P.I.D.) controller.

[0110] The P.I.D. controller may be arranged to control the flowrate ofthe liquid which is injected into the compressed gas in proportion tothe flowrate of the compressed gas.

[0111] The P.I.D. controller may be arranged to control the power outputof the gas turbine engine by controlling both the flowrate of the gasflowing through the gas turbine and the flowrate of the liquid which isinjected in to the compressed gas by the liquid injection means.

[0112] The method of the fifth and sixth aspects of the presentinvention may further include the step of controlling the flowrate ofliquid being injected into the compressed gas to control the poweroutput of the gas turbine engine.

[0113] The method of the fifth and sixth aspects of the presentinvention may further include the step of controlling the flowrate ofliquid which is injected into the compressed gas using the liquidflowrate control means.

[0114] The reciprocating and gas turbine engines of the first, third andfourth aspects of the present invention may each be arranged to drive ahydraulic pump/motor, generator, mechanical transfer means for thetransferral of mechanical energy, or one or more of the these incombination for controlling mechanical output from these engines.

[0115] The generator may be arranged to charge electrical storage meanswhich may in turn be arranged to power an electric motor.

[0116] Alternatively, the generator is preferably arranged to directlydrive an electric motor.

[0117] The hydraulic pump/motor may be arranged to drive the vehiclethrough hydraulic motors.

[0118] The reciprocating and gas turbine engines may each be arranged todrive a gearbox.

[0119] The gearbox of the gas turbine engine may have a step down ratioof approximately 6:1. The step down ratio of 6:1 may correspond to 35000rpm: 6000 rpm.

[0120] The gas turbine engine may be arranged to drive a wobble platetype hydraulic pump.

[0121] The vehicle may include the hydraulic pump/motor, generator,mechanical transfer means for the transferral of mechanical energy, orone or more of these in combination for controlling mechanical outputfrom the reciprocating or gas turbine engine.

[0122] The vehicle may also include the gearbox and a vehicle beingpowered by the gas turbine engine may also include the wobble plate typehydraulic pump.

[0123] The gearbox of the vehicle may be arranged to drive the hydraulicpump.

[0124] According to another aspect of the present invention there isprovided heat storage device comprising a container with an inlet, anoutlet, a heat storage substance and a heat transfer means, which isadapted to transmit fluid into the container for passage through theheat storage substance and discharge the fluid through the outlet.

[0125] Preferably the fluid is a gas.

[0126] The heat storage substance may comprise a molten chemicalcompound such as lithium chloride.

[0127] The fluid may be bubbled from the bottom of the container throughthe heat storage substance and out through the outlet.

[0128] The heat transfer means may comprise at least one conduit with atleast one outlet opening located at the bottom of the container.

[0129] In the preceding summary of the invention, except where thecontext requires otherwise, due to express language or necessaryimplication, the words“comprising”, “comprises”, or“comprise” are usedin the sense of “including”; that is, the features specified may beassociated with further features in various embodiments of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0130] A preferred embodiment of the present invention will now bedescribed, by way of example only, with reference to the followingdrawings in which:

[0131]FIG. 1 is a schematic sectional view of one example of areciprocating engine of the present invention;

[0132]FIG. 2 is a schematic flow diagram of one example of a gas turbineengine of the present invention; and

[0133]FIG. 3 shows an illustration of a heat cell according to oneembodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0134] Referring to FIG. 1, a reciprocating engine 10 generallycomprises a piston 12, displacer 14, cylinder 16, flywheel 18,connecting rods 20 and 22, a liquid salt heat cell and associated heatexchanger 24, a regenerator 26, a butterfly valve 28 and a heatexchanger 30. The piston 12 is designed to slide up and down along thelongitudinal length of the cylinder 16. An external cylindrical surfaceof the piston 12 seals against an inner cylindrical surface of thecylinder 16. The displacer 14 is a similar shape to the piston 12although it's upper surface is hemispherical to correspond to an upperinner surface of the cylinder 16. Unlike the piston 12, the displacer 14does not seal against an inside cylindrical surface of cylinder 16. Thedisplacer 14 is designed to move upwardly and downwardly along thelongitudinal length of the cylinder 16. The movement of the displacer 14and piston 12 relative to each other is controlled by their connectionthe flywheel 18. The piston 12 is connected to the flywheel by theconnecting rod 22 while the displacer 14 is connected to the flywheel 18by the connecting rod 20. The connecting rods 20 and 22 are attached tothe flywheel 18 so that the piston 12 and displacer 14 move within thecylinder 16 90° out of phase relative to each other.

[0135] Piston 12 divides the cylinder 16 into upper and lower ends orcompartments 32 and 34 respectively. Helium gas is contained within boththe upper and lower ends 32 and 34. The helium gas is also free to flowthrough cold and hot pipes 36 and 38 respectively which enable heliumgas from the cylinder 16 to flow through the regenerator 26, and theliquid salt heat cell and associated heat exchanger 24. The cold pipe 36extends approximately perpendicularly from the cylinder 16, about halfway along the longitudinal length of the cylinder 16 while the hot pipe38 extends upwardly of an up surface of the cylinder 16. The cold pipe36 connects the cylinder 16 with the regenerator 26 while the hot pipe38 connects the cylinder 16 with the liquid salt heat cell andassociated heat exchanger 24. The cold pipe 36 also continues beyond theregenerator 26 to connect the regenerator 26 with the liquid salt heatcell and associated heat exchanger 24.

[0136] The lower half of the cylinder 16 is attached to the heatexchanger 30 which is designed to remove heat from the lower half of thecylinder 16. The liquid salt heat cell and associated heat exchanger 24,in conjunction with the regenerator 26 and cold and hot pipes 36 and 38are designed to heat the helium gas which is contained within the upperend 32 of the cylinder 16. By heating the gas which is in the upper end32 of the cylinder 16 and cooling the gas which is in the lower end 34of the cylinder 16 the piston 12 reciprocates upwardly and downwardlywithin the cylinder 16 in accordance with the theoretical carnotcycle.The movement of the piston 12 results in rotation of the fly wheel 18.The engine 10 is therefore capable of converting heat energy intomechanical energy.

[0137] While the piston 12 and displacer 14 are connected to theflywheel 18, the moving piston 12 and displacer 14 could be used toproduce electrical energy rather than mechanical energy. Thisalternative would be possible by for example, attaching magnets to a rodsuch as the connecting rod 20 and allowing the rod to move forward andbackward through a coil. This alternative option would however require aspring or like item which is capable of initiating the upward movementof the piston 12. In the case of the embodiment depicted in FIG. 1, thisupward movement is provided by the momentum of the flywheel 18.

[0138] The reciprocating motion of the piston 12 and displacer 14 occursas a result of the following cycle. Helium gas from the upper end 32 ofthe cylinder 16 passes through the cold pipe 36, through the regenerator26, and into the liquid salt heat cell and associated heat exchanger 24.The heat exchanger that is associated with the liquid salt heat cell isdesigned to transfer heat from the liquid salt heat cell to the gaswhich passes through the heat exchanger. As the helium gas passesthrough the heat exchanger it is therefore heated and subsequently flowsthrough the hot pipe 38 and into the upper end of the cylinder 16. Thehot helium gas is able to flow down through the upper end 32 of thecylinder 16, between an outer side wall of the displacer 14 and an innerside surface of the cylinder 16. The hot gas 32 therefore fills theupper end 32 of the cylinder 16. Expansion of the hot helium gas resultsin forces being applied to both the piston 12 and displacer 14 andsubsequent downward movement of the piston 12 and displacer 14. As thepiston 12 and displacer 14 move downwardly the hot gas cools as a resultof the work that it has done on the piston 12 and displacer 14. As thegas is cooling it passes through the cold pipe 36 and into theregenerator 26. A generator is designed to absorb heat from the gaswhich passes through it. As the movement of the piston 12 and displacer14 continues within the cylinder 16 the gas within the cylinder 16 coolsfurther. When the piston 12 is at its lower most point within thecylinder 16 the cooling of the gas within the upper end 32 of thecylinder 16 results in a vacuum being created and the piston 12 beingdrawn upwardly within the cylinder 16. The upward movement of the piston12 is also facilitated by the momentum of the flywheel 18. As the piston12 moves upwardly, the cool gas which is contained within the upper end32 of the cylinder 16 passes out of the upper end 32 of the cylinder 16,through the cold pipe 36 and subsequently through the regenerator 26. Asthe cold gas passes through the regenerator 26 it absorbs heat from theregenerator 26 which has been absorbed from gas within the cylinder 16in a previous part of the cycle. The gas passing through the cold pipe36 is therefore preheated in the regenerator 26 prior to passing throughthe heat exchanger which is associated with the liquid salt heat cell.As the gas passes through the heat exchanger associated with the liquidsalt heat cell it is heated and as previously explained then passesthrough the hot pipe 38 and into the upper end of the cylinder 16 tocontinue the cycle.

[0139] The power output from the engine 10 can be controlled via thebutterfly valve 28. A butterfly valve 28 can be used to restrict theflowrate of gas flowing through the cold pipe 36 thereby restricting therate at which hot gas enters the upper end 32 of the cylinder 16. Suchrestriction of the flowrate of gas into the cylinder 16 results in thepower output from the engine 10 being reduced or throttled. Thebutterfly valve 28 can therefore be used to increase or decrease thepower output from the engine 10.

[0140] The displacer 14 has three main functions. It provides somedownward force which assists in rotating the flywheel, the rotation ofwhich provides momentum to the downward movement of the piston 12. Italso reduces the volume of the upper end 32 of the cylinder 16 meaningthat less expansion of hot gas is required to drive the piston 12downwardly. Finally, it acts as a heat sink which means that it assistsin heating the gas in the upper end 32 of the cylinder 16.

[0141] The liquid salt heat cell is a sodium fluoride liquid salt heatcell having a weight of approximately 2.97 tonnes. The liquid salt heatcell and associated heat exchanger 24 and regenerator 26 are designedfor the engine 10 so that the temperature and pressure within theregenerator 26, and liquid salt heat cell and associated heat exchanger24 do not exceed approximately 800° C., and between 15 and 25megapascals respectively.

[0142] A reciprocating engine 10 operating in this way can be used topower a vehicle. For an MRV, the liquid salt heat cell 14 is preferablycapable of providing 1000 kw of stored energy at a temperature rangingfrom 650 to 1000° C. Sodium chloride (NaCl), lithium fluoride (LiF) andsodium fluoride (NaF) are all capable of providing 1000 kw of energybetween 650 and 1000° C. and NaF appears to be the best compromisebetween reducing the amount or weight of salt required to provide 1000kw of energy while also minimising the cost. Approximately 2.97 tonnesof NaF is capable of satisfying the aforementioned design requirementsof a liquid salt heat cell for an MRV.

[0143] It is expected that the reciprocating engine 10 of FIG. 1 wouldbe capable of producing an output of approximately 100 kw. While such anoutput is capable of powering an MRV, it is advantageous that an MRV bepowered by a power source providing a larger output than this. The gasturbine engine 22 of FIG. 2 is capable of producing an output ofapproximately 236 kw and is therefore presently the preferred powersource for powering an MRV.

[0144] It is preferred that the reciprocating engine operates inaccordance with the sterling engine and includes an isothermalcompression, constant volume heating, isothermal expansion and constantvolume cooling in accordance with a carnotcycle with the work outputfrom the reciprocating engine being measured by the area enclosed by thecycle on a pressure-volume diagram.

[0145] Referring to FIG. 2, a humid gas turbine engine 40 generallycomprises a gas turbine 42, a NaF heat cell and associated heatexchanger 44, a recuperator 46, a gas to liquid heat exchanger 48, ahumidifier 49, a gas flowrate control valve 50 and a compressor 52. Thegas turbine engine 40 is a closed cycle gas turbine engine; exhaust gasexiting the gas turbine 42 is channelled into the compressor 52 whichthen pumps the exhaust gas back into the inlet side of the gas turbine42. The compressed helium gas which is pumped by the compressor 52, fromthe compressor 52 to the inlet side of the gas turbine 42, passesfirstly through the humidifier 49, then through the recuperator 46, andfinally through the NaF heat cell and associated heat exchanger 44,enroute the gas turbine 42. The gas which is pumped through the gasturbine engine 40 is Helium. The compressor 52 is designed to compressthe exhaust gas in accordance with the ratio 15:1.

[0146] The recuperator 46 is essentially a heat exchanger whichfunctions to transfer heat from the exhaust gas to the compressed gaswhich is subsequently pumped through the heat exchanger that isassociated with the NaF heat cell. The temperature of the exhaust gaswhich exists the gas turbine 42 is approximately 470° C. The temperatureof the gas exiting from the compressor 52 is approximately 400° C. Thehumidifier 49 decreases the temperature of the gas exiting thecompressor 52 to approximately 195° C. and the recuperator 46 raises thetemperature of the compressed gas to approximately 400° C. prior to itpassing through the heat exchanger that is associated with the NaF heatcell.

[0147] Pumping of compressed gas through the heat exchanger that isassociated-with the NaF heat cell results in the temperature of thecompressed gas being raised to a temperature of approximately 930° C.

[0148] After the exhaust gas passes through the recuperator 46 it is ata temperature of approximately 200° C. The exhaust gas is thereforerequired to pass through the gas to liquid heat exchanger 48 to reducethe temperature of the exhaust gas prior to it passing through thecompressor 52. The gas to liquid heat exchanger 48 reduces thetemperature of the exhaust gas to approximately 30° C. Cooling water 51is pumped through the gas to liquid heat exchanger 48.

[0149] The gas flowrate control valve 50 is positioned between the gasto liquid heat exchanger 48 and the compressor 52. The gas flowratecontrol valve 50 can be operated to throttle the gas turbine engine 40by restricting the flow of gas to the gas turbine 42. The gas flowratecontrol valve 50 is a vacuum/pressure pump which is modulated by acontrol system. Distilled water 53 is condensed out of the gas after itexits the gas to liquid heat exchanger 48 and before it passes throughthe gas flowrate control valve 50.

[0150] As explained above, the gas flowrate control valve 50 can be usedto decrease or increase power output 54 from the gas turbine 42.However, the power output 54 of the humid gas turbine engine 40 isimpaired if this method is used. By controlling the flowrate 56 ofdistilled water into the humidifier 49, it is expected that the poweroutput 54 will be able to be controlled without adversely effecting thepower output 54 of the gas turbine engine 40. A proportional integraldifferential (P.I.D.) controller would be suitable for controlling theflowrate 56 of the distilled water into the humidifier 49. The P.I.D.controller could control the flowrate of distilled water 56 inproportion to the gas flowrate control of the gas flowrate control valve50 so that the power output 54 is controlled via both the gas flowratecontrol valve 50 and the P.I.D. controller.

[0151] According to another embodiment of the present invention a fluidmay be injected into the humidifier 49 with the selection of the fluidmade to maximise the amount of heat which is able to be stored as latentheat as a part of the process of changing state from a solid to liquidand/or liquid to gas.

[0152] In order to lower the temperature of exhaust gas entering thecompressor 52 it is also envisaged that the gas to liquid exchanger 48be modified to include a pressurisation step which is able to lower thetemperature of the exhaust gas further. This may entail using a venturiarrangement at the outlet of the heat exchanger 48. In such a situationit is possible to dispense with the flow rate control valve 50.

[0153] It is preferred that the gas turbine operate in accordance withthe rate and cycle but in a modified form.

[0154] Although the preferred embodiment of the invention has beendescribed in relation to H2 _(o) it is also possible to use other fluidssuch as ammonia.

[0155] An Allison T63-A-700 (250-C18) gas turbine which produces anoutput of approximately 236 kw can be used to drive an MRV. Theestimated efficiency of the above described gas turbine engine 40 isapproximately 37%. The NaF heat cell is preferably capable of providing1000 kw of stored energy for the purpose of transferring heat to thecompressed gas at a temperature ranging from 650 to 1000° C. Asexplained above in relation to the reciprocating engine 10, 2.97 Tonnesof NaF is therefore required. The Allison gas turbine is connected to agearbox which has a step down ration of approximately 6:1 (35000 RPM to6000 RPM) which in turn is connected to a wobble plate type hydraulicpump which is designed to transfer power to tracks or wheels of the MRVthrough a series of hydraulic motors.

[0156]FIG. 3 shows a heat cell in accordance with one embodiment of thepresent invention. The heat cell 60 has a generally cylindrical shapewith a gas inlet 61 through a top section 62. The gas inlet 61 is acylindrical conduit which extends through the centre of the container 60and at the bottom thereof branches at 90° into conduit 63 havingopenings at each end.

[0157] The container is filled with a high temperature salt which isheated to a molten state. The container is made from a ceramic materialwhich is able to substantially prevent all heat from escaping frominside of the container.

[0158] A gas outlet 64 extends from the top section 62 of the container60.

[0159] In operation a gas is pumped through the conduit 61 and exitsthrough the ends of conduit 63 into the bottom of the container 60. Thegas, which is under pressure, bubbles through the molten salt which maybe lithium chloride and in the process absorbs heat. The gas then leavesthrough the gas outlet 64 at a considerably higher temperature.

[0160] The gas bubbling through the molten salt unit is in directcontact with the molten salt. This is in contrast to existing heat cellswhere heat must pass through a metal barrier in form of the heatexchange tubing.

[0161] It is expected that the heat transfer of the direct contactbubbling unit would be in the vicinity of a few hundred times higherthan conventional indirect contact tube heat exchangers. Furthermore itis expected that the cost of production of such a heat storage devicewould be significantly less than that of conventional heat storagedevices.

[0162] Because heat exchange tubing is not required the size of the heatcell can also be reduced.

[0163] According to another embodiment of the invention gas may bebubbled through the molten salt using alternative gas dischargingmethods.

1. A closed cycle gas turbine system comprising a compressor forproducing compressed gas, a gas turbine for receiving the compressedgas, a heat storage means having a first heat transfer means and adaptedto receive the compressed gas from the compressor and transmit thecompressed gas to the gas turbine and a second heat transfer means forreceiving exhaust gas from the gas turbine and transmitting it to thecompressor and wherein the second heat transfer means is adapted totransfer at least some heat from the exhaust gas prior to it beingtransferred to the compressor.
 2. The closed cycle gas turbine system asclaimed in claim 1 wherein the second heat transfer means is adapted totransfer heat from the exhaust gas to the compressed gas prior to thecompressed gas being received by the heat storage means.
 3. The closedcycle gas turbine system as claimed in claim 2 wherein the second heattransfer means comprises a recuperator.
 4. The closed cycle gas turbinesystem as claimed in claim 3 including a humidifier connected between anoutput of the compressor and an input of the heat storage means totransfer compressed gas therebetween.
 5. The closed cycle gas turbinesystem as claimed in claim 4 wherein the humidifier is adapted todecrease the temperature of gas exiting the compressor prior to it beingtransferred to the recuperator.
 6. The closed cycle gas turbine systemas claimed in claim 5 wherein the recuperator is adapted to raise thetemperature of gas received from the humidifier.
 7. The closed cycle gasturbine system as claimed in claim 6 including a controller forcontrolling flow rate of liquid to the humidifier.
 8. The closed cyclegas turbine system as claimed in claim 7 including a gas to liquid heatexchanger located between an output of the recuperator and an input ofthe compressor to thereby reduce the temperature of exhaust gas prior toits transfer to the compressor.
 9. The closed cycle gas turbine systemas claimed in claim 8 including a gas flow rate control valve which isadapted to control flow of exhaust gas to the gas turbine.
 10. Theclosed cycle gas turbine system as claimed in claim 9 wherein thecontroller includes a proportional integral differential (PID)controller which controls liquid into the humidifier based on flow rateof exhaust gas through the control valve.
 11. A vehicle having an engineincluding a closed cycle gas turbine system comprising a compressor forproducing compressed gas, a gas turbine for receiving the compressedgas, a heat storage means having a first heat transfer means and adaptedto receive the compressed gas from the compressor and transfer thecompressed gas to the gas turbine, a second heat transfer means forreceiving exhaust gas from the gas turbine and transferring it to thecompressor and wherein the second heat transfer means is adapted totransfer at least some heat from the exhaust gas prior to it beingtransferred to the compressor.
 12. The vehicle as claimed in claim 11wherein the second heat transfer means is adapted to transfer heat fromthe exhaust has to the compressed gas prior to it being received by theheat storage means.
 13. The vehicle as claimed in claim 12 wherein theclosed cycle gas turbine system includes a humidifier which is adaptedto receive compressed gas from the compressor and transfer thecompressed gas to the heat storage means via the second heat transfermeans.
 14. A reciprocating engine comprising a compartment having twoadjacent first and second sub compartments and at least one moveablepartition, the at least one moveable partition being arranged formovement to vary the volume of the adjacent sub compartments, the engineincluding heat storage means for heating a first gas which is containedwithin the first sub compartment relative to a second gas which iscontained within the second sub compartment, the engine including firstheat transferral means for transferral of heat from the heat storagemeans to the first gas, the at least one moveable partition beingarranged to cyclically vary the volume in the adjacent sub compartmentsas a result of heating of the first gas and consequently producemechanical energy, wherein the engine includes gas cycling means forcycling the first gas cyclically from the first adjacent sub compartmentto the first heat transferral means.
 15. The engine as claimed in claim14 wherein the gas cycling means includes a pipe.
 16. The engine asclaimed in claim 15 including a regenerator having heat absorption andrelease means for cyclically absorbing heat from the first gas andsubsequently transferring heat to the first gas upon cooling of thefirst gas.
 17. The engine as claimed in claim 16 wherein the regeneratorincludes a connecting portion which is arranged to transfer the firstand second gases between first and second adjacent sub-compartments ofthe regenerator.
 18. The engine as claimed in claim 17 including acylinder having the adjacent sub-compartments, a displacer being locatedwithin the compartment and connected to the moveable partition.
 19. Theengine as claimed in claim 18 wherein the moveable partition isconnected to a driving means for producing mechanical or electricalenergy.
 20. A vehicle including a reciprocating engine comprising acontainer having a compartment with adjacent first and secondcompartments separated by a moveable partition, an outlet and an inlet,a heat storage means, a heat transfer means and a conduit systeminterconnecting the outlet with the heat transfer means and the heattransfer means with the inlet, wherein heat from the heat storage meansis adapted to be transferred by the heat transfer means to gas withinthe conduit to drive the moveable partition to cyclically vary thevolume in the adjacent sub-compartments to enable cyclic circulation ofgas through the conduit system and the production of mechanical energyor electrical energy.
 21. The vehicle as claimed in claim 22 including aregenerator having heat absorption and release means for cyclicallyabsorbing heat from the gas and subsequently transferring heat to thegas once the gas has cooled.
 22. A heat storage device comprising acontainer having an inlet, an outlet, a heat storage substance and aheat transfer means which is adapted to transfer fluid into thecontainer whereby the fluid is able to pass through the heat storagesubstance and exit through the outlet.
 23. The heat storage device asclaimed in claim 22, wherein the gas is adapted to bubble through theheat storage substance.
 24. The heat storage device as claimed in claim23 wherein the heat storage substance is a molten salt compound.
 25. Theheat storage device as claimed in claim 24 wherein the heat transfermeans includes a conduit which extends to a bottom region of thecontainer and has outlet openings to enable discharge of the gastherefrom into the heat storage substance.